JP 2002-225733 A describes a steering-by-wire in which wheels are turned by one motor for steering. When the motor for steering malfunctions, a backup clutch is connected to mechanically couple a steering system. When turning by one motor in this way, the size of the motor increases to obtain a sufficient power, and thus the degree of freedom of the layout thereof are reduced. Therefore, it has been discussed to turn the wheels by two smaller motors.
The configuration in which the two motors turn the wheels is capable of suppressing the increasing in the size of the motor and is excellent in layout characteristics. However, there is a room for consideration about a fail-safe. For example, the backup clutch may be connected when any one of the motors malfunctions. However, this makes the other motor which does not malfunction unusable. Thus, the advantage of the provision of two motors is not fully utilized.